JIM LEHRER: The world nuclear summit wrapped up today in Washington. President Obama and other leaders pledged new action to keep nuclear weapons out of the hands of terror groups.

Jeffrey Brown begins our coverage.

JEFFREY BROWN: The president opened the second day of his nuclear security summit with a warning.

U.S. PRESIDENT BARACK OBAMA: Two decades after the end of the Cold War, we face a cruel irony of history — the risk of a nuclear confrontation between nations has gone down, but the risk of nuclear attack has gone up.

JEFFREY BROWN: After the president’s remarks, he and the leaders of 47 other countries went behind closed doors to talk about what they could do individually and collectively to secure nuclear materials. And, even while those talks continued, the administration could point to some progress on the sidelines of the summit.

WOMAN: Secretary of State Clinton and Russian Foreign Minister Lavrov are signing….

JEFFREY BROWN: This afternoon, Secretary of State Hillary Clinton and Russia’s foreign minister finalized a 10-year-old deal to reduce each country’s excess stocks of weapons-grade plutonium.

HILLARY RODHAM CLINTON, U.S. secretary of state: Under the agreement we are about to sign, the United States and Russia will each irreversibly and transparently dispose of no less than 34 metric tons of weapons-grade plutonium.

Together, that is enough material for nearly 17,000 nuclear weapons. And we will put in place the framework and infrastructure needed to dispose of even more plutonium from defense programs in the future.

JEFFREY BROWN: The U.S. also announced a deal with its North American neighbors to rid a Mexican nuclear reactor of its reliance on highly enriched uranium.

At the same time, yesterday’s meeting between President Obama and Chinese President Hu Jintao continued to draw attention and questions over the extent of China’s agreement to work with the U.S. on sanctions against Iran.

In Beijing today, a foreign ministry spokeswoman said sanctions aren’t the only solution to Iran’s nuclear ambitions.

JIANG YU, spokesperson, Chinese Foreign Ministry (through translator): We always believe that dialogue and negotiation are the best way out of the issue. Pressure and sanctions cannot fundamentally solve it. We believe relevant actions by the United Nations should be conducive to ease the situation there and conducive to pushing forward a solution through dialogue and negotiation.

JEFFREY BROWN: Iran insists its enrichment activities are peaceful, but the Obama administration is seeking tough sanctions to keep it from building nuclear weapons. Iran wasn’t invited to this week’s summit.

And today in Tehran, a foreign ministry spokesman said Chinese backing of a new round of sanctions was hardly assured.

RAMIN MEHMANPARAST, spokesperson, Iranian Foreign Ministry (through translator): We don’t consider such statements as their approval and support of the U.S. authority’s unjust measures, although we have repeatedly said that the issue of sanctions and going toward increasing sanctions is illogical and unfair and will not harm the Iranian nation’s will to achieve its rights.

JEFFREY BROWN: It was also revealed today that Secretary Clinton met privately last night with the permanent members of the United Nations Security Council and Germany to discuss the next steps on Iran.

Still, the president today kept the focus on the nuclear terrorism issue. And this afternoon, as the talks came to a close, he unveiled an agreement among all participating nations.

BARACK OBAMA: This evening, I can report that we have seized this opportunity, and, because of the steps we have taken, as individual nations and as an international community, the American people will be safer and the world will be more secure, that all the nations represented here have endorsed the goal that I outlined in Prague one year ago, to secure all vulnerable nuclear materials around the world in four years’ time.

JEFFREY BROWN: The communique makes each nation responsible for safeguarding nuclear materials and proposes a number of ways for the global community to work together against the sale or theft of such materials, while also recognizing that nations can continue to pursue peaceful nuclear energy programs.

Asked about Iran and sanctions, the president said he believes the Chinese are — quote — “serious” about supporting a tougher approach.

BARACK OBAMA: I think that, you know, a lot of countries around the world have trade relationships with Iran. And we’re mindful of that. But what I said to President Hu and what I have said to every world leader that I talk to is that words have to mean something. There have to be some consequences.

JEFFREY BROWN: The president also announced today that a follow-up nuclear security summit would take place two years from now in South Korea.

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